Meter for measurement of reflectance



Aug. 21, 1951 A. H. TAYLOR 2,565,151

METER FOR MEASUREMENT OF REFLECTANCE I Filed July 24, 1947 2Sheets-$heet1 v 7 f2 L lnvenbor-z AL gysi'us Hadley T691 1",

Aug. 21, 1951 A; H. TAYLOR METER FOR MEASUREMENT OF REFLECTANCE 2Sheets-Sheet 2 Filed July 24, 1947 Inventor: v Au g us"cus HadleyTaglor",

M a I M' His A'H'orneg;

Patented Aug. 21, 1951 METER. FOR MEASUREMENT OF REFLECTANCE AugustusHadley Taylor, Cleveland Heights, Ohio,

assignor to General Electric Company, a corporation of New YorkApplication July 24, 1947, Serial N0. 763,285

My invention relates to portable meters for measuring radiant energy andits principal object is to provide such a meter for measuring thereflectance of flat surfaces.

the following description of a species thereof and from the accompanyingdrawings in which Fig. l is a perspective view of the new meter; Fig. 2is an elevational view of the back of the meter with the back wallremoved; Fig. 3 is a sectional view taken along the line 3-3 of Fig. 4in the direction of the arrows; Fig. 4 is a side elevational, partlysectional view taken along the line 1 Claim. 25083) Further objects andadvantages of the invention will appear from ;4 of Fig. 3 with part ofthe side wall shown in elevation and with the back wall in place; and

Fig. 5 is a wiring diagram of the meter shown in Figs. 1 to 4.

Referring to Figs. 1 to 4 of the drawing the meter comprises a metalbox-like housing or casing l in which is mounted a U-shaped tubulardischarge lamp 2 supported by a socket 3 attached to the side wall 4ofthe housing I. The legs of the lamp- 2 are disposed in a common planeparallel with the back wall 5 of the housing and two light sensitivecells 6 and I are supported above and below the lamp 2 and between thelamp 2 and the back wall 5 of the housing by the angle brackets 8 (Fig.l). The light sensitive surfaces of the two cells 8 and l are in acommon plane parallel with the back wall 5 of the housing and face thesaid wall 5 which is in the form of a slide mounted in grooves 9 and In(Fig. 4) and provided with a finger grip II for ready removal from thehousing I. When measuring the reflectance of a flat surface the backwall '5 may be removed and the housing I may be held with its open backagainst the surface to block off light other than that from lamp 2. Withthe lamp 2 operating, the portion of the flat surface covered by the boxreflects light from the lamp 2 back toward the cells 6 and l which areconnected to the rheostat l2 and the microammeter l3 mounted on thefront wall I4 of the housing I with the turning knob l5 of the rheostatl2 and the dial face iii of the microammeter l3 on the outside of thefront wall M. The reflectance of the surface is easily read on the cali-2| on the outside of the wall. As shown at 20 and 20 of Fig. 5 switch 20is a double switch which connects the lamp 2 across a power source andmomentarily connects the lamp electrodes in series across the sourceduring starting. The lamp 2 is of the type disclosed in the U. S. Patent2,182,732 issued December 5, 1939 to Meyer etal. and comprises a base 22attached tothe spaced ends of a tubular U-shaped glass envelope whichtransmits radiation of 2537 A. wave length and contains a conductinggaseous atmosphere of argon or other rare gas andmercury vapor whichemits such radiation as well as radiation of other wave lengths when anelectric discharge is produced in the lamp. A pair of cooperating dis-,

charge supporting electrodes 23 and 24 (Fig. 5) are mounted at the endsof the lamp envelope. The meter may be used to measure the reflectanceof various kinds of flat surfaces for the 2537 A. wave length radiationemitted by the lamp 2 by properly constructing and connecting the lightsensitive cells 6 and I which receive such reflected radiation.

As shown in the wiring diagram of Fig. 5 the light sensitive cells 6 andI are connected in series in a closed circuit. The microammeter l3 andthe rheostat l2 are connected across the leads connecting the cells inseries and with the rheostat in shunt with the microammeter. The cellsare of the blocking or barrier layer type having a light sensitivesurface responsive to the 2537 A. wave length radiation and otherradiations emitted by the lamp. Such cells are available commerciallyand their characteristics are well known to those skilled in photometry.One cell has a cover of ordinary glass which does not transmit the 2537A. wave length radiation of the lamp while the other cell has a cover ofmaterial, such as quartz, which has a high transmission for suchradiation. The two cells 6 and 1 are electrically balanced before themeter is used so as to generate equal currents when exposed to radiationfrom the lamp having wave lengths longer than 3000 A. This may be doneby covering both the cells with a glass plate transparent to suchradiation and opaque to radiation of 2537 A. wave length and then, ifnecessary, adjusting the opaque strips 25 and 26 (Figs. 2 and 4) whichare clamped against support members 21 and 28 by strap 29 so that theymay be slid into position in front of the light sensitive surface of thecells 5 and I to mask part of the surface and block off therefrom moreor less of the reflected light transmitted by the glass plate to bringinto bal- 3 ance the current generated by the light sensitive surfacesof the cells 6 and 1. Thus, when the glass plate is removed the cellprovided with the quartz cover and responsive to the 2537 A. Wave lengthradiation generates a stronger current than the other cell. Thedifference in current generated by the cells is measured by themicroammeter I3 which is connected so as to match the polarity of thecell sensitive to the 2537 A. Wave length energy. The microammeter I3 iscalibrated so that the reflectance of the surface being measured may beread directly and compared with the reflectance of a standardreflectance plate.

The surface of the removable back wall 5 constitutes the standardreflectance plate of the meter. The rheostat l2 connected in shunt withthe microammeter i3 is provided for adjusting the latter while the lampis operating and the back wall in place until its indicating needle 36is brought to a marked index line on the dial face l6 which correspondsto the reflectance of the standard surface. With the back of the housingI held against the flat surface to be measured the back wall is removed.The reflectance of the surface to be tested may then be read on the dialface 16 of the microammeter l3 and compared with the reflectance of thestandard plate.

A handle 3| is provided on the top of housing I to facilitatetransportation of the meter.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

A portable meter for measuring the reflectance of a flat surface forradiation of 2537 A. Wavelength comprising a housing having an open backthe sides of which are adapted to engage the flat surface to be measuredand block off light from without the housing, the housing having aremovable wall covering said open back and having a surface of knownreflection for radiation of .2537 A. wavelength and which serves as astandard plate, a mercuryvapor ultraviolet lamp capable of emittingradiation of 2537 A. wavelength together with some radiations of longerWavelength and mounted in said housing in position to illuminate saidplate, a pair of lightsensitive surfaces substantially equidistant fromand on opposite sides of said lamp and substantially in a common planeparallel with said plate and facing away from the lamp and toward saidplate so that both said surfaces receive only reflected light of equalintensity, one of said cells having a cover of vitreous materialpervious to light radiations down to and including 2537 A. wavelength,the other cell having a cover of ordinary glass impervious to radiationsof 2537 A. Wavelength but pervious to radiations of longer wavelength, acurrent-measuring device mounted in said housing with its face exposedto view and being connected between the series connections between saidcells so as to measure the difference in current generated by therespective cells, said cells being equally sensitive to radiations ofwavelength longer than 3000 A. so they produce no deflection of saidcurrent-measuring device when both are exposed to such radiations, andan adjustable resistance connected electrically in parallel with saidcurrent-measuring device to adjust the current flow therethrough so thatthe scale deflection of the current-measuring device indicaes directlythe reflectance of the surface being tested for 2537 A. radiations.

AUGUSTUS HADLEY TAYLOR.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,778,000 Foulke Oct. 7, 19301,834,905 Sheldon Dec. 1, 1931 2,060,957 Tarvin et a1 Nov. 1'7, 19362,114,163 Bird Apr. 12, 1938 2,127,477 Carpenter et al. Aug. 16, 19382,349,754 Porter May 23, 1944 FOREIGN PATENTS Number Country Date646,511 Germany June 18, 1937

